CA1240024A - Color light signal using light emitting diodes - Google Patents

Abstract

ABSTRACT

A colour light signal especially adapted to railroad use has a cluster of diodes in place of a conventional incandescent source and each diode is located behind a collimating lens (the diodes may be located behind individual lenses or the entire cluster of diodes may be behind a single lens, if desired) and is positioned so the on-axis energy emitted from each diode is so directed that the combined wavefront is seen by the lens to originate at its focus, so that the dispersed energy is collimated into a signal beam of high-intensity and high directionality.

Description

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The present invention relates to an improved multi-colour light signal and particularly to an improved three-colour si~nal light of the type commonly placed beside railroad tracks and used for railway si~nalling.
BACKGRO~D OF THE I~E~TIO~
The usual searchlight si~nal used for railways employs only one tungsten lamp and one lens; nevertheless, the unit is designed to display three different colour aspects. The desired colour aspect is obtained mechanically by directing the light rays from the lamp through a red, green or yellow miniature roundel mounted near the circumference of a movable segmental disc positioned between the lamp and the signal lens. The segmental disc is the movin~ part of a three position type relay mechanism. The mechanism of the relay is arranged so that w~en de-energized, the disc will assume the nautral central position, with the red roundel directly in front of the lamp to give ths stop indication When the control circuit is energi ed in one direction, the disc rotates, the red roundel is moved away from its position and one of the other coloured roundels is moved into position in front of the lamp to ~ive a different colour indication.
A problem which is particularly prevalent in such conventional searchlight signalling devices is that the burnout of the tungsten signal lamp will result in an unlit si~nal which in certain circumstances results in delays in trains. To avoid this problem, the tungsten lamps are often replaced with new ones at regular short intervals as a means of preventative maintenance.
Another potentially dangerous problem, although rare, is the malfunction of the segmental disc which may result in the display of an improper light.
Okuno U.S. Patent ~o. b298869 issued November 3, 1981 describes and illustrates a light emitting diode (LED) display capable of emitting a large amount of coloured light. The LED display described and illustrated in that patent take3 the form of a direct replacement for an incandescent lamp where a ~- plurality of LEDs are mounted on a display unit ~aving a conventional lamp base such that the LED display can be used to replace the incandescent lamps without requiring modification of the structure. Such a construction, however, does not satisfy the optical characterlstics of the incandescent lamp which it replaces. The rays produced by the array of LEDs are too wide so that they do not appear optically as a point source. }lence such device cannot be used as direct replacement of the incandescent lamp for the conventional PAT 1423~

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searchlight commonly used for railway signalling.
A multi-coloured array of LEDs is taught by Teshima, et al in U.S. Patent No. ~,271,408 issued June 2, 1981. However, the inventors in that 2atent are clsarly concerned with relatively low li~ht-level applications such as pedestrian crossing signals and the li~e, since no effort is made to ensure that the rays of maximum bri~htness - which are emitted along the axes of the diodes - are collimated to provide the brightness levels required for railway signals. Indaed, Teshima, et al use reflectors behind the diodes, where practically no light emissi.ons take place. Again, the combined wavefront is approximately planar, which makes it impossible to collimate.
It is an ob~ect of the present invention to provide an improved light source for a multi-colour light si~nal which uses LEDs as a li~ht source. It is a further ob;ect of the present invention to provide such a light signal for railways which avoids the need for the mechanically operating discs to ~change the signal light colour generated by the device.
It is yet a further object of the present invention to provide an improved light source whereby the optical characteristics are comparable to the optical characteristics of the incandescent l~mp used in the conventional searchlight commonly used for railway signalling.
It is a further object of the present invention to provide an improved light source featuring long service life and which, even at the occurrence of partial failure, can continue to operate with no functionally significant drop in the visibility of the light source.
It is a further object of one aspect of the present invention to provide an improved LED light source which can be used in a conventional searchlight signal device without requiring modification of the structure.
SUMMARY OF THE INVE~TION
According to the present invention thare is providea an improved light source for a multi-colour signal light device having a light source mounted at one end of an inner assembly. The inner assembly provides a housing for electrical power circuits and connections to the device and is mounted in an outer housing having a protective collimating lens for the light source at the front of the device. A matrix of multi-colour light-emitting devices (LEDs) is provided mounted on a surface having a base. The LEDs which form the light unit are connected in groups of particular colours so that LEDs of each colour ~2~
group are simultaneous1y and exclusively illuminable to provide a light source of a particular colour. Heans are provided for directing on-axis energy from the diodes such that the centres of curvature of the wavefronts are concentrated a~ a point which coincides with the focal point o$ the protective collimating lens unit, whereby the wavefronts from the light source unit are converted into a signal beam having a dispersion angle and visibility suitable for the intended purpose of the device.
The signal light accordin~ to the present invention provides an LED li~ht source for signal li~hts, such as those used beside railway tracks. The construction according to the present invention provides such a signal light in which the LeDs appear as a point source. Its operation is entirely electrical in nature, requiring no mechanically operating component as did prior signal light devices. The L~Ds are preferably wired in a manner such that the failure of one or more LEDs of a particular colour ~roup will not result in a complete shut-down of the device as was the case with prior art tun~sten lamp signal lights; instead, while there will be a drop in the visibility of the light source for that particular color, the device may still continue to operate at least in a short term, until the LED matrix can be replaced.
BRIEF DESCRIPTIO~ OF THE DRAWI~GS
These and other objects and advanta~es of the invention will become apparent upon reading the following detailed description and upon referring to tha drawings in which:
Figure l illustrates a typical LED beam pattern;
Figure 2 is a schematic view of an example embodiment of the multi-colour signal light according to the present invention;
Fi~ure 2A is an e~ploded perspective view of the main components of the signal light of Figure l;
Figure 3 is a circuitry dia~ram showin~ the wiring of the multi-colour LED
matrix of the signal light according to the present invention;
Figure 4 is a block diagram of the alectronic layout of a signal light according to the present invention;
Figure 5 is a gide view of a LED with an ellipsoidal lens associated with it; and Pigure 6 is a schematic view of an alternative em~odiment of signal light

2~ -in accordance with the present invention, incorporating a plurality of LED's of Figure 5.
While the invention will be de~cribed in conjunction with example embodiments, i~ will be understood that it is not intended to limit the invention to such embodiments. One the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTIO~
In the following description, similar features in the drawings have been given similar reference numerals.
Figure l illustrates the beam pattern for a typical well-focused LED in terms of relativc bri~htness plotted against angular displacement from the diode axis. The point B indicates that peak brightness occurs at zero angular displacement and point A indicates that the brightness at the edge of the bsam has dropped to fifty per cent of peak at an angular displacement of about ten de~rees. It is thus an essential aspect of the present invention that the optics thereof collimate the light emitted from each diode "on-axis", in order to provide maximum intensity.
Turning to Figure 2, there is shown a schematic view of the optical design of the solid-state light signal 2, according to the present invention, suitable to be used as a light signal of the searchlight type and which is capable of selectively projecting single-colour beams of light of different, selected colours from a single light source. The device comprises an outer housing 4, a front convex protective collimating lens 6, an inner assembly 8, and power and control circuitry 10. The inner assembly 8 provides a housing for an optical means comprising a diverting lens 12, and for LED matrix 14.
LED matrix lb provides the light source for the light signal 2 so that by positioning and pointing the LED matrix 14 correctly through proper optics such as the double concave lens 12, it is possible to make all the LE~
wavefronts look like they came from a point source or through a point source even though the individual LED matrix produces a plurality of wavefronts.
According to the present inv2ntion, the diverging lens 12 is used to bend the combined wavefront emitted by the LED matrix 14 to fill the conventional collimating convex lens 6 such that the solid-state signal light could provide signal brightness equivalent to the conventional incandescent searchtype signal light. As illustrated in Figure 2, EED matrix 14 on a planar surface (optionally, as sho~n in phantom on a surface of revolution such as a spherical surface, etc.) is positioned behind double concave lens 12 so that the rays from the L~D matrix 14 appear to be diverged from a focal point which coincides with the focal point of the convex lens 6 used to collimate the wavefronts from the LED matrix 14 into a single beam. It is preferred for railway signal light applications, that the beam from lens 6 has a dispersion angle of less than 5 (preferably between 1.5 to 4), and be visible at at least 300 meters.
LED matri~ 1b is mounted on a base ring 16 (Eigure 2A) by means of legs 18. Adjustment means 20 are provided at the base ring 16 for the three-leg stand 18 so that the LED matrix 14 may be positioned and pointed correctly for the desired optical result. Base ring 16 enables the LED matrix 14 to be mounted on to the light source end of inner assem~ly 8 such that the LED
matrix 14 is properly positioned and spaced with respect to double concave lens 12. Ring 22 holds double concave lens 12 in place. Both the ring 22 and the double concave lens 12 are mounted inside the lens mount 24.
The LEDs for the LED matrix 14 are arranged in arrays and the LEDs within each array are connected electrically in series while the arrays are connected electrically in parallel ~roups as illustrated in Figure 3. The advantage of such an arrangement is that the si~nal light will continue to function albeit with reduced intensity even though malfunction or disconnection accidents may occur on some of the LEDs.
According to the present invention LED arrays, preferably of three different colours (red 26, yellow 28, green 30) com~ose the LED matrix 14 and are electrically connected so that the LEDs of each colour may be illuminated simultaneously and exclusively to provide the necessary signal colour for the signal li~ht. Preferably the number of LEDs in each array is substantially the same and the arrays are evenly spaced throughout the LED matrix lb in order to provide an evenly distributed luminous intensity of each colour.
The selection of a particular colour of LED arrays is logically controlled by the signal li~ht electronics as illustrated in the block diagram of Figure b. Light power 32 for the LEDs is provided by the power control circuit 34 which provides transient protection 36, rectifier filter function 38 and DC-DC
converter regulator function bO. The actual LED colour selection is .

PAT lb23-1 _ 5 _ controlled by the control logic 42 ~hich is composed of a transient protection circuit 44, optical isolation circuit 46 and a colour selection control eircuit b~. The colour selection control circuit also provides an output feedbac~ signal 52 ~o the external signal system b4 through the sense signal transient protection circuit 50. The supply of light power 32, the input signal to the control logic 42 and the output feedback signal 5~ are connections provided by the signal li~ht unit 2 to the external signal system 44.
As an alternative embodiment of the present invention shown in Figure 6, the proper optics for the LED matrix 14 can be achieved by providing a customized ellipsoidal lens 56 (Figure 6) for each individual LED of the LED
matrix 14. Hav~ng a customized ellipsoidal lens 56 mounted over each LED the light rays from the LED can be appropriately focused or collimated since the LED becomes relatively more like a point source with respect to the large diameter of the lens. Using this approach the optical arrangement speclally designed for the previously mentioned LED matrix 14, as illustrated in Figures 2 and 2A, is no longer required, simplifying the construction of the signal light unit 2. As illustrated in Figure 6, the signal light unit 2 of this embodiment consists of a regular transparent protective cover 60, the ellipsoidal lens-mounted LED matrix 52 and the control circuitry 10, all being housed inside the outer housing 4.
Thus it i5 apparent that there has been provided in arcordance with the invention an improved light signal device, that fully satisfies the objects, aims and advantages set orth above. While the invention has b0en described in coniunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will b~ apparent to those skilled in the art in light of the foregoing description. For example, coloured patterns produced according to conventional technology may be incorporated into the li~ht signal device according to the present invention to convey additional (close range) information. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the invention.

SUPPLE~ENTARY DISCLOSURE
The present invention is applicable to single-colour signals as ~ell as multi-colour signals. An arPa of interest using such a signal is that of ~grade-crossing.li~hts. Such lights are highly directional and have a relatively narrow beam-spread as well as hiSh intensiky.
In th additional drawing figures annexed hereto:
Figures 7 and 8 are ~chematic views of further example ~mbodiments of a multi-colour si~nal light according to the present invention;
Fi~ure 9 is an exploded perspective view of part of a further alternative embodiment of a signal light in accordance with the present invention, employing a plurality of converginS lenses associated with a matrix of LEDs.
Alternative embodiments of the invention are illustrated by Figures 7 and 8. The basic construction of the housing 4 and inner assembly 8 is simiLar to that of Figura 2 and the logic circuitry, etc. for driving the diodes 14 is similar. The essential difference between Figure 2 and Figures 7 and 8 is thzt the diverging lens 12 is dispensed with and the object of providing a combined wavefront from the LE~s, which appears to the conve~ lens 6 to have a single common source at the focal point f of the lens 6, is achieved by mounting the L~Ds 14 on a spherical array. In Figure 7, the LEDs are mounted on the concave surface of the ~pherical substrate and the light energy emitted on-axis from the diodes provides a ~ombined wavefront having a centre of curvature coincident with the focal point f of the lens 6. In Figure 8, the L~Ds 14 are mounted on the convex surface of the spherical substrate and the combin0d wavefront from the diodes a~ain appears to apparently ori~inatP from point f. In practice, the embodiment of Fi~ure 7 is somewhat more convenient from the viewpoint of the connection circuitry at the rear of the LED support substrate, which is easier to fabricate on a conve~ surface than on a concave æurface.
A variation of the embodiment of Fi~ure 6 is illustrated by the e~ploded view in Figure 9, and is especially suited to grade crossin~ lights or other warnin~ lights wherein hi~h directionality and luminance levels are requirad.
In this case, an array of diodes 212 is arranged upon a circula. board 213 and i~mediately in front Gf the board 213 is located by means of stand-offs 216 a second circular board 217, parallel to the board 213 and having an identical arrangement of converging lenses 218, so that each diode 212 is positionad PAT 1423~1 7 behind a lens 218 and coaxial therewith - the diode being locat~d at the focus of the lens. If desired, multiple LEDs may be located behind aach lens, with most of the transmitted li~ht originatin~ from diodes located at the focii of the lenses ~as.in Figure 9) and with other LEDs located in the focal plane of the lenses but off-axis, so that some li~ht is directed to one side of the warning light. This may be especially useful in the situation where the light is located on a curve, for example, and the s~condary light beams are aimed at traffic approaching the li~ht from an off-axis direction.

Claims (25)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a colour signal light device having a light source mounted in a housing having a protective collimating lens for the light source, the improvement characterized by a matrix of light emitting diodes (LEDs) mounted on a surface having a base means to secure the surface within the housing, the LEDs forming a light unit means, and means for directing the on-axis light energy from said diodes such that the combined wavefront has a centre of curvature which coincides with the focal point of the protective collimating lens to convert the dispersed energy from the light source unit into a substantially collimated signal beam having a dispersion angle and visibility suitable for the intended purpose of the signal light device.

2. A device according to claim 1, wherein said diodes are mounted upon a planar surface and a diverging lens is mounted between said array and said collimating lens, the plane of said diverging lens being parallel to said planar array and the focii of said diverging lens and said collimating lens being coincident so that on-axis light energy emitted from said diodes is passed through said diverging lens and said collimating lens to form a collimated beam.

3. A device according to claim 1, wherein said LEDs are arranged in groups of particular colours so that LEDs of each colour group are simultaneously and exclusively illuminable to provide a light source of a particular colour.

4. A device according to claim 3, further provided with a control logic means electronically associated with the LEDs for controlling the sequence of illumination of the groups of LEDs.

5. The device according to claim 3, wherein in each group of LEDs, a plurality of LEDs are connected in series and groups of the series are arranged in parallel.

6. A device according to claim 5, wherein the LEDs of each group are substantially the same number.

7. A device according to claim 5, wherein the LEDs of each group are spread substantially evenly throughout the matrix.

8. A device according to claim 5, wherein the LEDs are arranged on said surface in a plurality of arrays such that each array comprises a plurality of LEDs to emit light of a single colour, the LEDs of each colour being arranged substantially evenly throughout the surface area of a portion of the surface.

9. A device according to claim 8, wherein the plurality of arrays includes a first array of a first colour, a second array of a second colour and a third array of a third colour according to the sequence of signal lights required.

10. A device according to claim 9, wherein the first colour is red, the second colour is yellow and the third colour is green.

11. A device according to claim 1, wherein the base means has a predetermined shape adapted to effect mechanical mounting of the light unit to one end of an inner assembly forming the light source and mounted within said housing.

12. A device according to claim 10, wherein the base means has a circular ring base to effect mounting to the inner assembly and a raised stand which provided mounting means for the light unit at the top of the stand, the legs of the stand being adjustable connected to the circular ring base, and electric power connection means being associated with the circular ring base.

13. A device according to claim 4, wherein the control logic means comprises a logic circuitry to control the flow of electric power to the light unit and to cause simultaneous illumination exclusively of the LEDs of a particular group, as required, to generate a single colour signal light.

14. A device according to claim 2, wherein said diverging lens is a concave collector lens.

15. A device according to claim 1, 2 or 3, which provides a signal beam having a dispersion angle of less than five degrees and which is visible at at least three hundred meters in sunlight.

16. A device according to claim 1, 2 or 3, which provides a dispersion angle of between 1.5 degrees and 4 degrees.

17. A device according to claim 1, 2 or 3, wherein the light source is movably mounted in the inner assembly.

18. A device according to claim 1, wherein the surface is a surface of revolution.

19. A signal light device having a light source mounted in a housing having a protective transparent cover for the light source, the device being provided with a matrix of light emitting diodes (LEDs) mounted on a planar surface having a base means to secure the surface within the housing, an optical means comprising an elliptical lens being mounted over each LED and coaxial with the on-axis light emission from each said LED to provide collimated beams of light from said LEDs, in operation, the light from said LEDs and the optical means providing a signal beam having a dispersion angle and visibility suitable for the intended purpose of the signal light device.

20. A device according to claim 19 wherein the signal beam has a dispersion angle of less than five degrees and is visible at at least three hundred meters in sunlight.

CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE

21. A device according to claim 1, wherein said diodes are mounted upon a spherical surface having a centre of curvature coincident with the focal point of said collimating lens so that the on-axis light energy from said diodes is so directed that the combined wavefront has a centre of curvature coincident with said focal point and the dispersed energy passes through said collimating lens to form a collimated beam.

22. A device according to claim 21, wherein said surface is concave.

23. A device according to claim 21, wherein said surface is convex.

24. A signal light device having a light source mounted in a housing having a protective transparent cover for the light source, the device being provided with a matrix of light emitting diodes (LEDs) mounted on a planar surface having a base means to secure the surface within the housing, an optical means comprising a plurality of converging lenses mounted in front of said LEDs, the LEDs being in the focal plane of said lenses and said lenses being coaxial with the on-axis light emission from the respective LEDs to provide collimated beams of light from said LEDs, in operation, the light from said LEDs and the optical means providing a signal beam having a dispersion angle and visibility suitable for the intended purpose of the signal light device.

25. A device according to claim 24 wherein the signal beam has a dispersion angle of less than five degrees and is visible at at least three hundred meters in sunlight.